Solve 16
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1 changed files with 106 additions and 186 deletions
314
src/bin/16.rs
314
src/bin/16.rs
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@ -1,7 +1,9 @@
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use aoc::*;
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use glam::IVec2;
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use itertools::Itertools;
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use std::cmp::Ordering;
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use std::collections::{HashMap, HashSet};
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use std::{fmt, iter};
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use std::iter;
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const INPUT: &str = include_str!("../../input/16");
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@ -9,181 +11,121 @@ fn main() {
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assert_example!(part1, "16-test", 7036);
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println!("Part 1: {}", part1(INPUT));
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assert_example!(part2, "16-test", 45);
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// TODO Make part 2 terminate
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println!("Part 2: {}", part2(INPUT));
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}
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fn part1(input: &str) -> usize {
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let mut maze = Maze::parse(input);
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maze.solve();
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maze.best_score()
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let maze = Maze::parse(input);
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maze.dijsktra().lowest_score(maze.end)
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}
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fn part2(input: &str) -> usize {
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let mut maze = Maze::parse(input);
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maze.solve();
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maze.good_seats()
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Maze::parse(input).good_seats()
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}
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#[derive(Clone, Debug)]
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struct Tile {
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pos: IVec2,
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visited: bool,
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score: usize,
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direction: Direction,
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}
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impl Tile {
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fn new(pos: IVec2) -> Self {
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Self {
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pos,
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visited: false,
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score: usize::MAX,
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direction: Direction::East,
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}
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}
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visited: bool,
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previous: Vec<(IVec2, Direction)>,
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}
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struct Maze {
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start: IVec2,
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end: IVec2,
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walls: HashSet<IVec2>,
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tiles: HashMap<IVec2, Tile>,
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tiles: HashSet<IVec2>,
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}
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impl Maze {
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fn solve(&mut self) {
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loop {
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let next = self
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.tiles
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.values()
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.filter(|t| !t.visited)
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.min_by_key(|t| t.score);
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let Some(next) = next.cloned() else {
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break;
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};
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self.tiles.insert(
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next.pos,
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Tile {
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visited: true,
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..next
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},
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);
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for dir in Direction::ALL {
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let neighbor = next.pos + dir.vec();
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let Some(neighbor) = self.tiles.get_mut(&neighbor) else {
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continue;
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};
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if neighbor.visited {
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continue;
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}
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let new_score = if dir == next.direction {
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next.score + 1
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} else {
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next.score + 1001
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};
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if new_score < neighbor.score {
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neighbor.score = new_score;
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neighbor.direction = dir;
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}
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}
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}
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// println!("===");
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// let size = self.tiles.iter().fold(IVec2::ZERO, |a, b| a.max(*b.0));
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// for y in 1..=size.y {
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// for x in 1..=size.x {
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// let pos = IVec2::new(x, y);
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// let tile = self.tiles.get(&pos).map(|t| t.score).unwrap_or(0);
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// print!("{tile:>6}");
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// }
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// println!();
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// }
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}
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fn best_score(&self) -> usize {
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self.tiles.get(&self.end).unwrap().score
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}
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fn good_seats(&self) -> usize {
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self.good_seats_rec(
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self.best_score(),
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0,
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HashSet::new(),
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Direction::East,
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self.start,
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)
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let dijkstra = self.dijsktra();
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let endings = dijkstra
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.0
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.iter()
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.filter(|((pos, _), _)| *pos == self.end)
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.min_set_by_key(|(_, tile)| tile.score);
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endings
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.into_iter()
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.map(|(end, _)| dijkstra.good_seats(*end))
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.fold(HashSet::new(), |mut a, b| {
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a.extend(b);
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a
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})
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.len()
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}
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fn good_seats_rec(
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&self,
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target_score: usize,
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score: usize,
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mut visited: HashSet<IVec2>,
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dir: Direction,
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pos: IVec2,
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) -> HashSet<IVec2> {
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if score > target_score {
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return HashSet::new();
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fn dijsktra(&self) -> Dijkstra {
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let mut maze: HashMap<(IVec2, Direction), Tile> = self
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.tiles
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.iter()
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.copied()
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.cartesian_product(Direction::ALL)
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.zip(iter::repeat(Tile {
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score: usize::MAX,
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visited: false,
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previous: Vec::new(),
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}))
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.collect();
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maze.insert(
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(self.start, Direction::East),
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Tile {
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score: 0,
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visited: false,
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previous: Vec::new(),
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},
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);
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loop {
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// Pick unvisited with minimal distance
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let next = maze
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.iter()
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.filter(|(_, tile)| !tile.visited)
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.min_by_key(|(_, tile)| tile.score)
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.map(|(&k, v)| (k, v.clone()));
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let Some(((pos, dir), current)) = next else {
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break;
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};
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// Mark visited
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maze.insert(
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(pos, dir),
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Tile {
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visited: true,
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..current
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},
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);
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// Update neighbors
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let update_neighbor = |add: usize| {
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let new_score = current.score + add;
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move |neighbor: &mut Tile| match new_score.cmp(&neighbor.score) {
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Ordering::Less => {
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neighbor.score = new_score;
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neighbor.previous = vec![(pos, dir)];
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}
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Ordering::Equal => {
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neighbor.previous.push((pos, dir));
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}
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Ordering::Greater => {}
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}
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};
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maze.entry((pos + dir.vec(), dir))
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.and_modify(update_neighbor(1));
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maze.entry((pos, dir.rotate_cw()))
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.and_modify(update_neighbor(1000));
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maze.entry((pos, dir.rotate_ccw()))
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.and_modify(update_neighbor(1000));
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}
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if !self.tiles.contains_key(&pos) {
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return HashSet::new();
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}
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if visited.contains(&pos) {
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return HashSet::new();
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}
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visited.insert(pos);
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if score == target_score && pos == self.end {
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return visited;
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}
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let mut result = HashSet::new();
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{
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result.extend(self.good_seats_rec(
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target_score,
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score + 1,
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visited.clone(),
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dir,
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pos + dir.vec(),
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));
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}
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{
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let new_dir = dir.rotate_cw();
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result.extend(self.good_seats_rec(
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target_score,
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score + 1001,
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visited.clone(),
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new_dir,
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pos + new_dir.vec(),
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));
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}
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{
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let new_dir = dir.rotate_ccw();
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result.extend(self.good_seats_rec(
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target_score,
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score + 1001,
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visited.clone(),
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new_dir,
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pos + new_dir.vec(),
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));
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}
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result
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Dijkstra(maze)
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}
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fn parse(input: &str) -> Self {
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let mut start = IVec2::ZERO;
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let mut end = IVec2::ZERO;
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let mut tiles = HashMap::new();
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let mut walls = HashSet::new();
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let mut tiles = HashSet::new();
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let input = input
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.lines()
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@ -194,60 +136,49 @@ impl Maze {
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match c {
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'S' => {
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start = pos;
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tiles.insert(
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pos,
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Tile {
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pos,
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visited: false,
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score: 0,
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direction: Direction::East,
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},
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);
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tiles.insert(pos);
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}
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'E' => {
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end = pos;
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tiles.insert(pos, Tile::new(pos));
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}
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'#' => {
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walls.insert(pos);
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tiles.insert(pos);
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}
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'#' => {}
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'.' => {
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tiles.insert(pos, Tile::new(pos));
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tiles.insert(pos);
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}
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other => panic!("unknown tile: '{other}'"),
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}
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}
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Self {
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start,
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end,
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walls,
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tiles,
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}
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}
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}
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impl fmt::Display for Maze {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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let size = self.walls.iter().fold(IVec2::ZERO, |a, b| a.max(*b));
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for y in 0..=size.y {
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for x in 0..=size.x {
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let pos = IVec2::new(x, y);
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if self.walls.contains(&pos) {
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write!(f, "█")?;
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} else if let Some(t) = self.tiles.get(&pos) {
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write!(f, "{}", t.direction)?;
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} else {
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write!(f, "?")?;
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}
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}
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writeln!(f)?;
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}
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Ok(())
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Self { start, end, tiles }
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}
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}
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#[derive(Copy, Clone, Debug, PartialEq, Eq)]
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struct Dijkstra(HashMap<(IVec2, Direction), Tile>);
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impl Dijkstra {
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fn lowest_score(&self, at: IVec2) -> usize {
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Direction::ALL
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.into_iter()
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.map(|dir| self.0.get(&(at, dir)).unwrap().score)
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.min()
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.unwrap()
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}
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fn good_seats(&self, current: (IVec2, Direction)) -> HashSet<IVec2> {
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let current_tile = self.0.get(¤t).unwrap();
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let mut seats = HashSet::from([current.0]);
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for &prev in ¤t_tile.previous {
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seats.extend(self.good_seats(prev));
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}
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seats
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}
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}
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#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
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enum Direction {
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North,
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East,
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@ -290,14 +221,3 @@ impl Direction {
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}
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}
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}
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impl fmt::Display for Direction {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match self {
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Self::North => write!(f, "^"),
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Self::East => write!(f, ">"),
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Self::South => write!(f, "v"),
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Self::West => write!(f, "<"),
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}
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}
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}
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